U.S. Pat. No. 5,342,886 discloses polymer blends comprising a compatibilizer and more particularly blends of polyamide and of polypropylene. The compatibilizer is composed of a polypropylene backbone to which are attached polyamide grafts. This compatibilizer is prepared from a polypropylene homopolymer or copolymer (the backbone) to which maleic anhydride is grafted. Separately, polyamide with a monoamine ending, that is to say having an amine end and an alkyl end, is prepared. Then, by melt blending, the monoamino polyamide will become fixed to the polypropylene backbone by reaction between the amine functional group and the maleic anhydride.
Patent WO 9950323 discloses an improvement of the preceding prior art. According to this prior art, 3-isopropenyl-α,α-dimethylbenzyl isocyanate (TMI) of following formula:
is grafted to the polypropylene backbone, the fixing of the TMI to the backbone being carried out via the double bond. The amount of grafted TMI is at most 1.8 parts by weight per 100 parts of the backbone. Caprolactam and sodium caprolactomate as catalyst are then added. Anionic polymerization of the caprolactam is thus carried out, which polymerization begins and grows starting with the isocyanate functional group which has been grafted onto the polypropylene backbone. The isocyanate functional group acts as activator for this polymerization. However, as the polymerization of the caprolactam to form the grafts is very slow, it is necessary to add activator in addition to the isocyanate but, in addition to the compatibilizer, PA 6 homopolymer is manufactured.
It has now been found that it is no longer necessary to add activator in addition to the isocyanate grafted onto the polypropylene backbone provided that the amount of grafted TMI is at least 2 parts by weight per 100 parts of backbone. The caprolactam polymerizes essentially starting from the isocyanate activator and the compatibilizer comprising essentially no PA 6 homopolymer is obtained.
It has also been found that it is possible to manufacture compatibilizers composed of a polyolefin backbone to which are fixed polyamide grafts using other polyolefin backbones and/or other monomers for the fixing and the growth of the polyamide grafts.